Joystiq ran a poll to see how many of its readers are high definition ready. Out of the 5,495 voters, 41% said they were HD ready, 48% said they were not, and 11% said they will be HD ready soon.
I think the numbers are a bit off, and they should definetly not be taken as the number for the national average, but for a gaming community, I would assume they are atleast close to right.
That is not too bad, as those with HD will be able to take full advantage of next-generation gaming consoles, while those without will still be able to take part, but it will be more about the gameplay than the fancy high definition graphics.